How Clearly Defined Is the Border between France and Spain?

No one lives on little Pheasant Island, stuck in the middle of the Bidasoa River bordering France and Spain. It’s peaceful there, with trees and neatly trimmed grass. There’s also an old monument that marks the Treaty of the Pyrenees, a peace agreement signed in 1659 by representatives of both countries, followed by a royal wedding, where King Louis XIV of France married the daughter of King Philip IV of Spain. An unusual part of the agreement called for joint ownership of the island, alternating between French rule and Spanish rule every six months.

A different kind of condominium:

In French, Pheasant Island is known as Île des Faisans. In Spanish, it’s called Isla de los Faisanes.

Spain assumes sovereignty of the island every February, and the French take the reins every August. This joint sovereignty is called a condominium.

As of January 2018, the island is approximately 660 feet (200 m) in length and 130 feet (40 m) in width, but erosion is taking a toll.